Effect of verapamil on contractility, oxygen utilization, and calcium exchangeability in mammalian heart muscle

Environmental contaminants modulate transport activity of zebrafish (Danio rerio) multidrug and toxin extrusion protein 3 (Mate3/Slc47a2.1)

Zebrafish Mate3 is one of six co-orthologs of human multidrug and toxin extrusion proteins. It is highly expressed in the kidneys, intestine, testes, and brain of males. Initial interaction studies showed its interaction with xenobiotic compounds, suggesting a role in the efflux of toxic compounds. In this study, we aimed to test various environmental contaminants for their interaction with zebrafish Mate3. We developed a stable zebrafish Mate3 cell line and optimized a high-throughput screening assay using DAPI and ASP+ as fluorescent model substrates. To gain insight into the structure and function of the Mate3 protein and relate these to the results of the DAPI and ASP+ transport measurements, we predicted its 3D structure using the AlphaFold2 algorithm. A 3D structure with high per residue confidence scores with 13 transmembrane segments (TMs) was obtained, with topology and mutual positioning characteristic of the Mate protein family in a shape open to the extracellular part. Molecular docking methods were used to identify DAPI and ASP+ binding sites on the surface and in the center of the protein cavity. Because our kinetics experiments combined with molecular docking indicated that there may be additional active sites in zebrafish Mate3, additional cytotoxicity experiments were performed and highly potent Mate3 interactors were identified from a set of 55 different environmental contaminants. Our results suggest that some of the identified interactors may be of environmental concern, as their interaction with Mate3 could lead to an impairment of its normal efflux function, making fish more sensitive to harmful substances commonly released into the aquatic environment. Finally, the quality of zebrafish Mate3 structures predicted by the AlphaFold2 algorithm opens up the possibility of successfully using this tool for in silico research on transport preferences of other Mate proteins.

Calcium Channel Blockers in Acute Care: The Links and Missing Links Between Hemodynamic Effects and Outcome Evidence

Calcium channel blockers (CCBs) exert profound hemodynamic effects via blockage of calcium flux through voltage-gated calcium channels. CCBs are widely used in acute care to treat concerning, debilitating, or life-threatening hemodynamic changes in many patients. The overall literature suggests that, for systemic hemodynamics, although CCBs decrease blood pressure, they normally increase cardiac output; for regional hemodynamics, although they impair pressure autoregulation, they normally increase organ blood flow and tissue oxygenation. In acute care, CCBs exert therapeutic efficacy or improve outcomes in patients with aneurysmal subarachnoid hemorrhage, acute myocardial infarction and unstable angina, hypertensive crisis, perioperative hypertension, and atrial tachyarrhythmia. However, despite the clear links, there are missing links between the known hemodynamic effects and the reported outcome evidence, suggesting that further studies are needed for clarification. In this narrative review, we aim to discuss the hemodynamic effects and outcome evidence for CCBs, the links and missing links between these two domains, and the directions that merit future investigations.

Treatment of calcium channel blocker-induced cardiovascular toxicity with drug scavenging liposomes

Calcium channel blocker (CCB) overdose is potentially lethal. Verapamil and diltiazem are particularly prone to acute toxicity due to their dual effect on cardiac and vascular tissues. Unfortunately, conventional decontamination measures are ineffective in accelerating blood clearance and, to date, few efforts have been made to develop antidotes. To address the issue, injectable long-circulating liposomes bearing a transmembrane pH-gradient are proposed as efficient detoxifying agents of CCB poisoning. By scavenging the drug in situ, these circulating nanocarriers can restrict its distribution in tissues and hinder its pharmacological effect. In vitro, we showed that liposomes stability in serum and their ability to sequester CCBs could be finely-tuned by modulating their internal pH, surface charge, and lipid bilayer structure. Subsequently, we verified their efficacy in reversing the cardiovascular effects of verapamil in rats implanted with telemetric pressure/biopotential transmitters. In animals orally intoxicated to verapamil, an intravenous injection of the liposomal antidote rapidly attenuated the reduction in blood pressure. Areas under diastolic, systolic, and mean pressures curves were significantly reduced by up to 60% and the time to hemodynamic recovery was shortened from 19 to only 11 h. These findings confirm the protective effect of pH-gradient liposomes against cardiovascular failure after CBB intoxication, and endorse their potential as efficient, versatile antidotes.

On the mechanism of action of calcium antagonists

A short review is given of possible mechanisms of action of the organic "calcium antagonists". Calcium antagonists comprise a chemically heterogenous group of drugs, and the term may be used to denote agents that inhibit Ca2+-dependent processes or regulatory mechanisms without acting at other sites. Such drugs may be subdivided into those that decrease the availability of Ca2+ to the myoplasm, and those that decrease the cellular effects of Ca2+ without lowering the intracellular Ca2+ concentration. Accordingly, calcium channel blockers, such as verapamil, nifedipine, and diltiazem, form a subgroup of calcium availability inhibitors, as they block influx of extracellular calcium through ion selective channels in the membrane both in cardiac and smooth muscle. However, it cannot be excluded that some of these drugs, particularly in smooth muscle, may have additional sites of action, which must be taken into consideration when they are used as investigational tools.

Effect of nifedipine (Adalat) on coronary haemodynamics in patients with coronary arteriosclerotic disease

Effects of the new Ca++ antagonist nifedipine (Adalat) on coronary haemodynamics were studied in 8 patients with documented ischaemic heart disease. The continuous infusion thermodilution technique was used to measure cardiac venous blood flow. Sublingual application of 10 mg nifedipine caused a significant increase (16%) in myocardial blood flow and a decrease (18%) in coronary arteriolar resistance at rest, but not during a submaximal atrial pacing test. There was no change in coronary arteriovenous oxygen difference, myocardial oxygen consumption, oxygen consumption per unit of heart rate blood pressure index or left ventricular efficiency index. The effects on the coronary haemodynamics are discussed in relation to the simultaneous changes in general haemodynamics. Systolic aortic pressure was slightly reduced, significantly only at rest, while peripheral vascular resistance decreased and cardiac output increased also during atrial pacing. No change in free fatty acid metabolism was observed. It is concluded that nifedipine is a mild coronary vasodilator. No effect was observed on myocardial oxygen demand. The oxygen cost of left ventricular work was unchanged by the drug both at rest and during the submaximal stress test.

Calcium antagonists

Calcium antagonists were introduced for the treatment of hypertension in the 1980s. Their use was subsequently expanded to additional disorders, such as angina pectoris, paroxysmal supraventricular tachycardias, hypertrophic cardiomyopathy, Raynaud phenomenon, pulmonary hypertension, diffuse esophageal spasms, and migraine. Calcium antagonists as a group are heterogeneous and include 3 main classes--phenylalkylamines, benzothiazepines, and dihydropyridines--that differ in their molecular structure, sites and modes of action, and effects on various other cardiovascular functions. Calcium antagonists lower blood pressure mainly through vasodilation and reduction of peripheral resistance. They maintain blood flow to vital organs, and are safe in patients with renal impairment. Unlike diuretics and beta-blockers, calcium antagonists do not impair glucose metabolism or lipid profile and may even attenuate the development of arteriosclerotic lesions. In long-term follow-up, patients treated with calcium antagonists had development of less overt diabetes mellitus than those who were treated with diuretics and beta-blockers. Moreover, calcium antagonists are able to reduce left ventricular mass and are effective in improving anginal pain. Recent prospective randomized studies attested to the beneficial effects of calcium antagonists in hypertensive patients. In comparison with placebo, calcium antagonist-based therapy reduced major cardiovascular events and cardiovascular death significantly in elderly hypertensive patients and in diabetic patients. In several comparative studies in hypertensive patients, treatment with calcium antagonists was equally effective as treatment with diuretics, beta-blockers, or angiotensin-converting enzyme inhibitors. From these studies, it seems that a calcium antagonist-based regimen is superior to other regimens in preventing stroke, equivalent in preventing ischemic heart disease, and inferior in preventing congestive heart failure. Calcium antagonists are also safe and effective as first-line or add-on therapy in diabetic hypertensive patients. Heart rate-lowering calcium antagonists (verapamil, diltiazem) may have an edge over the dihydropyridines in post-myocardial infarction patients and in diabetic nephropathy. Thus, calcium antagonists may be safely used in the management of hypertension and angina pectoris.

Antihypertensive drugs and the sympathetic nervous system

The sympathetic nervous system (SNS) plays an important role in the regulation of blood pressure homeostasis and cardiac function. Furthermore, the increased SNS activity is a predictor of mortality in patients with hypertension, coronary artery disease and congestive heart failure. Experimental data and a few clinical trials suggest that there are important interactions between the main pressor systems, i.e. the SNS, the renin-angiotensin system and the vascular endothelium with the strongest vasoconstrictor, endothelin. The main methods for the assessment of SNS activity are described. Cardiovascular drugs of different classes interfere differently with the SNS and the other pressor systems. Pure vasodilators including nitrates, alpha-blockers and dihydropyridine (DHP)-calcium channel blockers increase SNS activity. Finally, central sympatholytics and possibly phenylalkylamine-type calcium channel blockers reduce SNS activity. The effects of angiotensin-II receptor antagonists on SNS activity in humans is not clear; experimental data are discussed in this review. There are important interactions between the pressor systems under experimental conditions. Recent studies in humans suggest that an activation of the SNS with pure vasodilators in parallel increases plasma endothelin. It can be assumed that, in cardiovascular diseases with already enhanced SNS activity, drugs which do not increase SNS activity or even lower it are preferable. Whether this reflects in lower mortality needs to be investigated in intervention trials.

Differential activation of cardiac and peripheral sympathetic nervous system by nifedipine: role of pharmacokinetics

OBJECTIVES

We sought to study the effects of short-acting and long-acting nifedipine on the sympathetic nervous system (SNS), heart rate (HR) and blood pressure (BP) of normotensive subjects under baseline conditions and during SNS stimulation.

BACKGROUND

Calcium channel antagonists in different pharmacokinetic formulations are widely used in patients with coronary artery disease or hypertension. Short-acting formulations activate the SNS, an action that may be disadvantageous in patients with coronary disease, especially if left ventricular function is impaired. The effects of slow-release formulations on the SNS are unknown.

METHODS

We used microneurography to investigate the influence of nifedipine (5 mg; 10 mg; and slow-release [GITS], 60 mg) on muscle sympathetic nerve activity (MSA) and skin sympathetic nerve activity (SSA) in healthy volunteers.

RESULTS

Peak plasma levels after short-acting and slow-release nifedipine were achieved within 60 min and 330 min, respectively. Short-acting (10 mg, n = 10) and slow-release (n = 10) nifedipine, but not placebo, markedly activated MSA and increased plasma norepinephrine; plasma endothelin increased only with slow-release nifedipine. HR increased after short-acting nifedipine, but not after nifedipine GITS. Nifedipine had no effect on SSA (n = 6). Blockade of cardiac sympathetic activity (with esmolol) led to similar decreases in HR with or without nifedipine, whereas parasympatholysis (with atropine) led to similar increases in HR with or without nifedipine. The cold pressor test markedly increased MSA in all treatment groups and further increased MSA beyond the increase induced by nifedipine.

CONCLUSIONS

Nifedipine markedly increased MSA, but not SSA, independently of drug release formulation. In contrast, HR increased with short-acting, but not with slow-release, nifedipine. Therefore, nifedipine activates cardiac and peripheral sympathetic nerves differently depending on pharmacokinetics. These effects of nifedipine may be disadvantageous in cardiac patients with increased sympathetic activity or congestive heart failure, or both.

Cardiac effects of calcium antagonists in systemic hypertension

The calcium antagonists are a class of heterogeneous drugs, with a wide spectrum of direct and indirect cardiac effects that vary a great deal from one drug to another and depend upon formulation and duration of action. Calcium antagonists act by decreasing total peripheral resistance to lower arterial pressure. As a consequence, reflex tachycardia, increased cardiac output, and increased plasma catecholamine and plasma renin activity are commonly seen, particularly with the initial dose and with short-acting dihydropyridines. The abrupt vasodilation can paradoxically elicit angina and even acute myocardial infarction. These hemodynamic and neuroendocrine changes are less pronounced with the long-acting formulations. Most calcium antagonists diminish automaticity of the sinus node, slow conduction in the atrioventricular node, and have little, if any, effect on the automaticity of the myocytes. The dihydropyridines generally have less effect on automaticity and cardiac conduction than nondihydropyridines. The negative inotropic effect is most profound with nondihydropyridines and is greatly reduced or absent with newer dihydropyridines, such as isradipine, felodipine, amlodipine, and nisoldipine. Long-acting calcium antagonists generally improve myocardial oxygenation by unloading the heart, increasing coronary blood flow, and reducing myocardial oxygen consumption. Thus, calcium antagonists have a variety of beneficial effects in patients with hypertensive heart disease: they reduce left ventricular hypertrophy and its sequelae, such as ventricular dysrhythmias, impaired filling and contractility, and myocardial ischemia. Ongoing studies should provide a more conclusive answer regarding the efficacy and safety of calcium antagonists.

Inhibition of [3H]-U69593 binding and the cardiac effects of U50, 488H by calcium channel blockers in the rat heart

1. The calcium channel blockers (CCBs), nifedipine, nicardipine, diltiazem and verapamil, were used to displace the binding of [3H]-U69593 ((5a, 7a,8b)-(+)-N-methyl-N-(7-[1-pyrrolidinyl]-1-oxaspiro[4,5] dec-8-yl)-benzeneacetamide), a specific kappa-opioid agonist, in the rat cardiac sarcolemma. The CCBs competed with the binding of [3H]-U69593 (4 nM) in a dose-dependent manner. The displacing potency of verapamil was 55 times greater than that of nifedipine. 2. The effects of two CCBs, verapamil and nifedipine, on the arrhythmogenic action of kappa-receptor stimulation by a specific kappa-receptor agonist, U50,488H (trans-(+/-(-3),4-dichloro-N-methyl-N-(2-[1-pyrrolidinyl] cyclohexyl) benzeacetamide methanesulphonate), were also studied in the rat isolated perfused heart. U50,488H 80-800 nmol dose-dependently induced arrhythmias, which were completely abolished by a selective kappa-receptor antagonist, nor-BNI (nor-binaltorphimine, 17,17'-(dicyclopropylmethyl)-6,6',7,7'-6,6'-imino-7,7'-binorphinan -3,4',14, 14'-tetrol), at 100 nmol. The arrhythmogenic effect was also attenuated by both verapamil and nifedipine in a dose-dependent manner. The ED50 values for verapamil and nifedipine were 2.75 and 63.7 nmol, respectively. The antiarrhythmic potencies of these two CCBs were correlated to their displacing potencies and inversely related to their well known potencies in inhibiting transmembrane Ca2+ influx in the cardiac muscle. 3. Measurement of [Ca2+]i in the absence of free extracellular Ca2+ by a spectrofluorometric method, with fura-2 as Ca2+ indicator, showed that U50,488H 5 x 10(-5) M slowly increased [Ca2+]i in single ventricular myocytes and this effect was abolished by pretreatment with nor-BNI (5 microM), or ryanodine (5 microM). Verapamil 1 and 10 microM abolished the effect of U50,488H in 37.5% (3 out of 8) and 100% (12 out of 12) of the cells studied, respectively. On the other hand, nifedipine 10 and 100 microM had no effect at all. Neither verapamil nor nifedipine exerted any significant effect on the caffeine-induced Ca2+ transient. 4. The observations suggest that CCBs may inhibit the actions of kappa-receptor stimulation at the level of the kappa-receptor.

Effect of gallopamil on excitation-contraction coupling

1. Investigations performed in skeletal muscle have suggested that phenylalkylamine calcium antagonists, particularly gallopamil, affect excitation-contraction coupling independently of their effect on the sarcolemmal calcium current. 2. Sarcoplasmic reticulum and single channel studies have provided evidence that phenylalkylamine calcium antagonists inhibit calcium release through the sarcoplasmic reticulum calcium channel/ryanodine receptor. This action has not been observed with dihydropyridine calcium antagonists. 3. Binding experiments have confirmed the existence of intracellular binding sites for phenylalkylamines, and have shown that gallopamil interferes with the binding of ryanodine to its low affinity sites. 4. The dose-response relationship for the effect of gallopamil on excitation-contraction coupling has not been definitely established. However, there is evidence that gallopamil may be effective at concentrations that are close to the therapeutic range.

Effect of verapamil on restoration of cardiac performance in raised [K+]o by adrenergic stimulation in the rabbit

Modulation of the L-type calcium channel by catecholamines improves action potential parameters in single ventricular myocytes depolarized by high [K+]o Tyrode. Whether this modulation is important in offsetting the negative effects of hyperkalaemia in the whole heart is not known. We tested the effects of the calcium channel antagonist, verapamil, on restoration of cardiac performance by adrenergic stimulation in high [K+]o in anaesthetized rabbits and isolated perfused working rabbit hearts. Raised [K+]o decreased SBP, LVP and LVdP/dtmax in vivo ([K+]a 8.6 +/- 0.2 mM; n = 10) and aortic flow (AF) in the isolated heart (8 mM [K+]o Tyrode; n = 25). However, the negative effects of raised [K+]a were offset by isoprenaline (Iso, 1 microgram kg-1 min-1 i.v.) in vivo and by noradrenaline (NA, 80 nM) in the isolated heart. Verapamil (0.15 mg kg-1 i.v.; 15 nM isolated heart) markedly potentiated the negative inotropic effects of raised [K+]o in both preparations. Verapamil attenuated the effect of isoprenaline in vivo but in the isolated heart, the protective effect of NA in 8 mM [K+] Tyrode (AF 97 +/- 10 mL min-1 in 8 mM [K+]o compared with AF 141 +/- 8.5 mL min-1 in 8 mM [K+]o + NA) was offset by the drug (90 +/- 8 mL min-1 in 8 mM [K+]o + NA + V). Furthermore, verapamil abolished aortic flow in 8 mM [K+]o alone. These findings suggest that the heart may be critically dependent on modulation of intracellular calcium in order to tolerate concentrations of K+ similar to those seen during a short burst of intensive exercise ([K+]a 8.6 mM).

Comparative haemodynamic effects of verapamil, flecainide, amiodarone and sotalol in the conscious rabbit

1. The effect of intravenous boluses of verapamil (0.15 mg/kg), flecainide (2 mg/kg), amiodarone (5 mg/kg), and sotalol (1.5 mg/kg) on mean arterial pressure, heart rate (HR), cardiac output (CO), total peripheral resistance (TPR), and peak rate of change of left ventricular pressure (LV dP/dt) were assessed in the conscious rabbit. 2. All four drugs had negative inotropic effects: verapamil reduced peak LV dP/dt by 19 +/- 4% (mean +/- s.e.m.; P < 0.01), flecainide by 27 +/- 9% (P < 0.001), amiodarone by 11 +/- 2% (P < 0.01) and sotalol by 13 +/- 3% (P < 0.01). 3. The drugs had different effects on CO as a result of differences in their actions on peripheral blood vessels: verapamil and amiodarone produced, respectively, a 12 +/- 4% (P < 0.03) and 16 +/- 6% (P < 0.01) increase in CO associated with a substantial vasodilatory effect (TPR reduced 15 +/- 7% [P < 0.05] and 20 +/- 5% [P < 0.01], respectively). Flecainide caused only a small (6 +/- 1%; P < 0.01) increase in CO and sotalol had no effect on either CO or TPR. 4. Bolus intravenous injections of verapamil, flecainide and amiodarone produced an increase in HR, while sotalol reduced HR by 10 +/- 2% (P < 0.01). The increase in HR and cardiac output seen with verapamil, flecainide and amiodarone was in part secondary to reflex increase in sympathetic tone and these changes were abolished after total cardiac autonomic blockade. 5. The modest reduction in cardiac performance associated with sotalol was abolished by cardiac autonomic blockade, suggesting that the predominant effect of sotalol on contractility was mediated through its beta-adrenoceptor blocking effect.

Electrical and mechanical alternans in canine myocardium in vivo. Dependence on intracellular calcium cycling

BACKGROUND

Electrical and mechanical alternans are thought to result from a common cellular mechanism. To confirm this phenomenon in vivo and extend our understanding, we investigated the effects of temperature, verapamil, and caffeine on alternans in intact beating hearts.

METHODS AND RESULTS

We recorded surface ECG, monophasic action potential (MAP) using suction electrodes, and left ventricular pressure (LVP). Alternans of MAP configurations and of LVP were evaluated in 20 dogs. MAPs were recorded from the apex, base, and midportion of the left ventricle with LVP. The hearts were driven from the left ventricular apex at a basic cycle length of 1000 milliseconds, and alternans was induced with an abrupt shortening of the cycle length to 400 milliseconds. MAPD30/100, the ratio between the MAP durations (MAPD) at 30% and 100% repolarization levels, was measured as an index of MAP configuration. The magnitude of MAP or LVP alternans was defined as the difference in MAPD30/100 or in LVP between the fifth and sixth paced beats. The magnitude of MAP alternans differed by recording site but correlated with activation time. Lowering the temperature increased the magnitude. MAP alternans was always associated with LVP alternans under control conditions. Verapamil significantly attenuated the magnitude of MAP alternans but did not change that of LVP alternans. Caffeine attenuated the magnitude of both MAP and LVP alternans. T wave alternans was suppressed by verapamil or caffeine.

CONCLUSIONS

Activation time is one of the factors modifying electrical alternans. Delayed intracellular Ca2+ cycling plays a role in the concomitant occurrence of electrical and mechanical alternans.

Interactions between verapamil and metoprolol in the developing chick embryo heart

A calcium blocking agent, verapamil, and a beta 1-adrenoreceptor blocking agent, metoprolol, were administered alone or in combination to 4-day-old chick embryos (Hamburger-Hamilton developmental stage 24). Embryos co-administered with verapamil (0.05 nmol) and metoprolol (0.1 or 1.0 nmol), neither of which alone caused significant teratogenicity, showed cardiovascular malformations, including ventricular septal defects associated with or without dextroposition of the aorta (overriding aorta). The alterations of calcium movement into the myocyte and/or the haemodynamic change following impaired calcium transport are suggested to be possible causative factors.

Chronic calcium channel blockade prevents the progression of myocardial contractile and electrical dysfunction in the cardiomyopathic Syrian hamster

The programmed onset of myocardial dysfunction and its progression to congestive heart failure in the cardiomyopathic Syrian hamster is hallmarked by alterations in myocellular calcium regulation. To determine whether calcium channel blockade is effective in halting the progressive depression of myocardial contractile performance in this animal model of congestive heart failure, oral verapamil therapy was instituted at 50 days of age, and treatment continued for various durations until the time of study at either 150 or 250 days of age. Left ventricular papillary muscle isometric and isotonic performance, as well as transmembrane electrical characteristics, was depressed in diseased hamsters at 150 days of age and deteriorated further by 250 days of age. These changes were evidenced by prolongation of contraction duration, a marked depression in the load-velocity relation, and a significant prolongation in the repolarization phase of the transmembrane action potential. Myocardial functional and electrical alterations associated with the progression of life in myopathic hamsters were completely halted by verapamil therapy that was continuous from 50 days after birth until death by diastolic arrest, at 150 or 250 days of age. However, premature termination of verapamil treatment before death resulted in a progressive renewal of the functional and electrical alterations for the duration of drug termination. It is concluded that the pathological changes seen during the lifetime of the cardiomyopathic hamster can be prevented by continuous calcium channel blockade and that intermediate prevention can be attained by protracted verapamil therapy. Thus, chronic verapamil therapy may be a useful adjunct in the prevention of human congestive heart failure of similar etiology.

Direct binding of verapamil to the ryanodine receptor channel of sarcoplasmic reticulum

Radioligand binding experiments and single channel recordings demonstrate that verapamil interacts with the ryanodine receptor Ca2+ release channel of the sarcoplasmic reticulum of rabbit skeletal muscle. In isolated triads, verapamil decreased binding of [3H]Ryanodine with an IC50 of approximately 8 microM at an optimal pH 8.5 and pCa 4.3. Nitrendipine and d-cis-diltiazem did not interfere with binding of [3H]Ryanodine to triads, suggesting that the action of verapamil does not involve the dihydropyridine receptor. Single channel recordings showed that verapamil blocked Ca2+ release channels by decreasing open probability, duration of open events, and number of events per unit time. A direct interaction of verapamil with the ryanodine receptor peptide was demonstrated after purification of the approximately 400 kDa receptor protein from Chaps-solubilized triads. The purified receptor displayed high affinity for [3H]Ryanodine with a Kd of approximately 5 nM and a Bmax of approximately 400 pmol/mg. Verapamil and D600 decreased [3H]Ryanodine binding noncompetitively by reducing the Bmax. Thus the presence of binding sites for phenylalkylamines in the Ca2+ release channel was confirmed. Verapamil blockade of Ca2+ release channels may explain some of the paralyzing effects of phenylalkylamines observed during excitation-contraction coupling of skeletal muscle.

The role of calcium antagonists in the management of renal warm ischemia

Eighty dogs with solitary kidneys were used to investigate the effects of calcium antagonists on the functional capacity and structural integrity of kidneys subjected to sixty minutes of warm ischemia by transient vascular occlusion under general anesthesia. Treated dogs were compared with control animals who had normal or untreated ischemic kidneys (group 1 and 2) and also with saline-flushed ischemic kidneys without or with heparinization (group 3 and 4). Verapamil and nicardipine were used independently as local (group 5 and 7) or systemic treatment (group 6 and 8). Functional and structural studies revealed that calcium antagonists improved animal survival, renal hemodynamics, renal functional capacity, cellular adenine nucleotides, and reduced the ischemic structural damage. Local treatment of ischemic kidneys with 0.15 mg. nicardipine afforded the best protection against the deleterious effects of renal warm ischemia.

Effects of verapamil on intracellular lipid accumulation in cat hearts with 3 h of regional-ischaemia

In the regionally ischaemic heart lipid droplet accumulation is found in the ischaemic area and is most pronounced in the periphery. The purpose of the present study is to explore the potential effects of the calcium-channel-blocker verapamil on this accumulation. The drug is known to reduce the intensity of myocardial ischaemic injury. The myocardial ultrastructure was studied in anaesthetized open chest cats with 3 h of coronary artery occlusion. Biopsies were taken from the ischaemic, border and normally perfused myocardium defined in vivo injections of fluorescein and verified by blood flow measurements using radiolabelled microspheres. Arterial concentration of non esterified fatty acids (NEFA) was measured during the ischaemic period. A higher accumulation of lipid droplets was found in the central ischaemic myocardium of verapamil-treated cats than in control animals (p less than 0.05). The normally perfused and borderline areas were unaffected by verapamil as far as lipid accumulation was concerned and showed the same pattern as in the untreated group. The increased accumulation of lipid droplets in the ischaemic myocardium, after treatment with verapamil, may reflect a preserved metabolic activity in the ischaemic tissue or result from a higher supply of fatty acids due to increased perfusion of the central ischaemic tissue.

The Ca2+ -antagonist and binding properties of the phenylalkylamine, anipamil

1. Isolated, Langendorff-perfused rat hearts, isolated membranes, and pharmacological and receptor binding techniques were used to study the properties of the newly developed verapamil derivative, anipamil. 2. When added acutely to isolated, spontaneously beating or electrically paced hearts, anipamil (0.01-0.15 microM) exerted a dose-dependent negative inotropic effect which developed slowly and persisted after 60 min washout. 3. When added acutely (0.05-0.1 microM) to isolated hearts, or when given intravenously (2 mg kg-1 body weight 1 h before the animals were killed), anipamil displaced the dose-response curves for the positive inotropic effect of (0.10-3.0 mM) Ca2+ and (10-50 nM) Bay K 8644 to the right. 4. When added to freshly isolated cardiac membranes, 0.1 microM anipamil increased the dissociation constant (KD) of the phenylalkylamine (-)-[3H]-desmethoxyverapamil ((-)-[3H]-D888) from 1.22 +/- 0.2 to 2.91 +/- 0.46 nM, without any significant change in density (Bmax; control: 163 +/- 17; anipamil: 117 +/- 20 fmol mg-1 protein). Bound (-)-[3H]-D888 was displaceable by (-)-D888 (Ki 1.7 +/- 0.4 nM) greater than (-)-D600 (Ki 12 +/- 0.5 nM) greater than verapamil (Ki 55 +/- 11 nM) greater than (+)-D600 (Ki 108 +/- 12.2) greater than anipamil (Ki 471 +/- 52 nM). 5. In cardiac membranes isolated from rats pretreated with anipamil (2 mg kg-1 i.v.) 1h before they were killed, the KD of (-)-[3H]-D888 binding was increased (P less than 0.05) from 1.59 +/- 0.18 to 3.28 +/-0.65 nM with no significant change in density, compared to the placebo-treated (control) rats. 6. These results establish that anipamil interacts in a competitive manner with the phenylalkylamine binding sites in cardiac membranes, and that it resembles other Ca2+ antagonists in displacing the dose-response curve for the positive inotropic effect of Ca2+ to the right. The results also show that although anipamil binds tightly to the cardiac membranes, it binds to the (-)-[3H]-D888 recognition sites less potently than (-)-D888, (-)-D600 or verapamil.

Fundamental mechanisms of action of calcium antagonists in myocardial ischemia

The mammalian myocardium exhibits a spectrum of damage during an ischemic episode. After relatively short periods of ischemia the damage is reversible, but with longer periods of ischemia the number of cells that are lethally injured increases. When coronary flow is restored the lethally injured cells become overloaded with Ca++ and fail to regenerate adenosine triphosphate. The calcium antagonists provide protection under these circumstances, but only if used prophylactically. When added only upon reperfusion the calcium antagonists slow, but do not inhibit, the excessive gain in Ca++ that occurs during postischemic reperfusion. Nicotine, in a concentration equivalent to that found in the plasma of smokers (0.15 microgram/ml), exacerbates the reperfusion-induced Ca++ gain. Treatment with the long-acting calcium antagonist, anipamil, on a once-daily basis attenuates the reperfusion-induced Ca++ gain in spontaneously hypertensive rats and its exacerbation by nicotine in Sprague Dawley rats. The prolonged oral administration of at least 1 calcium antagonist, verapamil (50 mg/kg body weight/day), causes a significant (p less than 0.001) depletion of left ventricular norepinephrine.

The influence of verapamil and papaverine on the calcium- and epinephrine-induced responses of isolated guinea-pig atria

The effects of papaverine and verapamil on Ca2+ - and epinephrine evoked responses were investigated on spontaneously beating atria of the guinea-pig. Papaverine showed a non competitive antagonism against epinephrine but was ineffective against Ca2+; verapamil antagonized both the action of epinephrine and Ca2+ in a different manner but at the same concentrations. The pharmacological prerequisite to classify an anti-Ca2+ substance as a blocker of Ca2+ entry (that is the ability to selectively antagonize the Ca2+ -induced contraction relative to those of norepinephrine in vascular smooth muscle) was not met by the results obtained in the cardiac tissue. The behaviors of verapamil and papaverine with regard to Ca2+ response suggest another criterion for classifying a substance as a Ca2+ entry blocker based on the ability or inability to inhibit the response of the atrial preparation to Ca2+.

Effects of verapamil on ischemia-induced changes in extracellular K+, pH, and local activation in the pig

In experimental animals, the calcium channel-blocking agents lessen the arrhythmogenic, ionic, metabolic, and electrical changes that occur during acute myocardial ischemia. To date, these effects have been studied separately, and the effects of these agents on local activation have not been correlated with ionic or metabolic effects. In open-chest, anesthetized swine, we used bipolar and ion-selective plunge electrodes to simultaneously measure ischemia-induced changes in left ventricular local activation, extracellular K+ ([K+]e), and extracellular pH (pHe). The effects of verapamil (0.2 mg/kg) on these variables were studied during a series of 10 min occlusions of the left anterior descending coronary artery. Compared with control occlusions, verapamil (1) slowed the rise in [K+]e at the center of the ischemic zone and at its lateral margin and decreased the peak [K+]e by 0.9 mM at the center (p less than .05) and by 0.1 mM at the margin (p = .10); (2) slowed the development of acidosis and decreased the peak level of acidosis beyond that expected solely as a result of serial occlusions by 0.19 pH units at the center (p less than .05) and by 0.07 pH units at the margin (p = .10); and (3) slowed the development of local activation delay and often prevented the local activation block that was observed during control occlusions. Effects on local activation became less marked at [K+]e levels greater than 9.0 mM, and the effects of verapamil on local activation were not explained solely by its effects on the local rise in [K+]e or fall in pHe. A possible mechanism for this additional effect on local activation is suggested by preliminary results showing a diminution by verapamil of ionic inhomogeneity.

Effects of calcium channel blockers on ouabain-induced oscillatory afterpotentials in organ-cultured young embryonic chick hearts

Ouabain induces oscillatory afterpotentials (OAPs) in organ-cultured young (3 day old) embryonic chick hearts. Since increased [Ca]i resulting from an inhibition of the Na pump by ouabain triggers oscillatory movements of Ca2+ (i.e. OAPs) intracellularly, Ca2+ influx through the cell membrane, which tends to increase [Ca]i, may be important in developing the OAPs. Therefore, in the present experiments, effects of calcium channel blockers on ouabain-induced OAPs in organ-cultured 3 day old embryonic chick hearts were examined. Automaticity was suppressed by elevating [K]o to 6 mM. To induce the OAPs, the preparations were stimulated (0.5 Hz) in the presence of ouabain (2.5-6.3 microM). The calcium channel blockers (10 microM) depressed the OAPs in the following order of potency: bepridil greater than verapamil greater than nifedipine greater than diltiazem. This order of potency of the calcium channel blockers in depressing the OAPs was the same as that for drug penetration into the cells, but different from that for depressing slow action potentials: nifedipine greater than diltiazem greater than verapamil greater than bepridil (our previous findings). These results suggest that an intracellular site of action of the calcium channel blockers is important for depression of the OAPs, and suppression of the slow inward Ca2+ current cannot be the sole mechanism for suppression of the OAPs by these drugs.

Calcium dependency and free calcium concentrations during insulin secretion in a hamster beta cell line

Using a glucose-responsive beta cell line, we tested the hypothesis that the free cytosolic Ca2+ concentration ([Ca2+]i) is the primary signal that couples a stimulus to insulin secretion, and examined the involvement of the extracellular Ca2+ pool in this process. Glucose or depolarization of the beta cell with 40 mM K+ stimulated a monophasic release of insulin directly proportional to the extracellular Ca2+ concentration. 40 mM K+ increased 45Ca2+ uptake and increased [Ca2+]i, which was measured with quin 2, 4.7-fold, from 56 +/- 3 to 238 +/- 17 nM. With high glucose, 45Ca2+ uptake did not increase, and [Ca2+]i was unchanged or fell slightly. There was a striking correlation between inhibitory effects of verapamil, the Ca2+ channel blocker, on insulin secretion and the rise in [Ca2+]i evoked by K+. Higher concentrations of verapamil were required to inhibit glucose- than K+-stimulated insulin secretion (dose giving half-maximal effect of 1.4 X 10(-4) M vs. 6.0 X 10(-7) M). Incubation in Ca2+-free, 1 mM EGTA buffer for 30 min lowered [Ca2+]i to 14 +/- 2 nM, and inhibited acute insulin release to both secretagogues. If high glucose was present in the Ca2+-free period, reintroduction of 2.5 mM Ca2+ in high glucose restored insulin secretion only to the basal rate. However, if low glucose was present during the Ca2+-free period, high glucose and 2.5 mM Ca2+ triggered a full first-phase insulin response. These data suggest that high glucose generates a non-Ca2+ signal that turns over rapidly and provide direct evidence that K+ triggers insulin release by drawing extracellular Ca2+ into the beta cell through verapamil-sensitive Ca2+ channels. However, an increase [Ca2+]i is not the primary signal that evokes glucose-stimulated insulin release in this beta cell line.

Short- and long-term treatment of mild to moderate hypertension with verapamil

Forty-three patients with mild to moderate hypertension (supine diastolic blood pressure 95 to 115 mm Hg) were entered into a short-term (3 months) study. All received verapamil, 120 mg 3 times a day. After 1 month of treatment on verapamil alone, supine diastolic blood pressure was normalized (less than 95 mm Hg) in 29 patients (67%). These patients continued with verapamil at the same dosage. In 14 nonresponders (supine diastolic blood pressure greater than 95 mm Hg) a combination of althiazide (15 mg/day) and spironolactone (25 mg/day) was added. This resulted in diastolic blood pressure normalization in 9 additional patients. Verapamil induced a slight but moderate decrease in heart rate after 1 month, but no further decrease was observed thereafter. During the trial, 21% of patients reported adverse effects, mostly transient and mild. No patient had to discontinue treatment because of them. Twenty-six patients on verapamil alone were followed for 1 year. Systolic and diastolic blood pressure was adequately controlled in all patients except 1. In 13 the dosage was decreased to 120 mg 2 times a day. There were no significant differences in blood pressure between this group and patients given 120 mg 3 times a day. It is concluded that verapamil is an effective and safe antihypertensive agent in mildly to moderately hypertensive patients. Because a dosage of 120 mg 2 times a day was as effective as 120 mg 3 times a day, the former should be recommended, as it may improve patient compliance.

Ontogenetic differences in cardiac sensitivity to verapamil in rats

The degree of a negative inotropic response of the isolated right ventricle to verapamil as well as the mortality rate were studied in rats during their postnatal development. Male Wistar rats aged 3, 15, 30, and 90 days were used. The isolated right ventricle was incubated in a glucose-free solution with a mixture of 95% O2 and 5% CO2 and electrically stimulated. The amplitude of isotonic contractions (AIC) was registered. In 90-day-old rats, AIC was 74.1 +/- 6.2% of initial amplitude 45 min after administration of verapamil; in 30-day-old, 41.1 +/- 6.4%; in 15-day-old, 38.2 +/- 4.1%; and in 3-day-old rats, only 2.6 +/- 1.5. The difference between the 3-day-old rats and all older groups was statistically highly significant. The mortality rate of verapamil-treated rats increased with decreasing age of animals. It is concluded that the sensitivity of the rat myocardium to verapamil is age dependent: the negative inotropic effect of this drug increases with decreasing age of the animal. This indicates a possible risk in the therapeutic use of verapamil when given to newborns and infants.

The influence of verapamil on dopamine's ability to augment cardiac output

Calcium channel blockers are used in the treatment of angina pectoris, cardiac arrhythmia, and hypertension. Sporadic reports of hypotensive reactions to verapamil have indicated that these reactions are not reversed readily by catecholamine administration. This study was conducted to test the hypothesis that verapamil pretreatment does not alter the ability of dopamine in conventional doses to augment cardiac output. Twelve mongrel dogs, weighing 19 to 25 kg, were anesthetized with pentobarbital and placed on a respirator. Heart rate, cardiac output, and the right atrial, pulmonary artery, pulmonary capillary wedge, and central aortic pressures were measured directly. Dopamine, 10 micrograms/kg/min, increased cardiac index by 52.4 mL/kg/min over baseline. The dopamine was stopped and the animals were allowed to return to baseline. Dopamine, 10 micrograms/kg/min, was administered again after pretreatment with 0.15 mg/kg verapamil, and it increased cardiac index by 47.9 mL/kg/min over the second baseline control. The results were not statistically different using the Student t test for paired data (P greater than .05). It is concluded that verapamil does not affect dopamine's ability to augment cardiac output in the dosages tested.

Potentiation by calcium channel blockade of hypoxic myocardial depression in the neonate

The objectives of this study were to examine the independent and combined effects of beta blockade (practolol) and calcium channel blockade (verapamil) on cardiac responses to hypoxia in the neonate. Lambs were anaesthetized with pentobarbital (20 mg/kg) and were prepared for measurements of left ventricular (LV) performance under controlled hemodynamic conditions. Force generation was assessed from curves relating LV systolic pressure (SP) to end-diastolic pressure (LVEDP) over a broad range of afterloading. Velocity was determined from simultaneous measurements of LV dP/dtmax. Values obtained at LVEDP 10 cm H2O were used to compare interventions. Practolol (P) caused no significant reduction in SP10, but dP/dt10 fell from 51 to 37 (X 10(2] mm Hg/sec (p less than 0.05). Verapamil (V), 2 micrograms/min/kg, reduced measures of contractility (p less than 0.01). Doubling the dose of V further reduced SP10 to 79% of control. Hypoxemia (PaO2, 32 torr) increased SP10 from 172 to 192 mm Hg, and dP/dt10 from 51 to 85 (X 10(2] mm Hg/s (p less than 0.001). After P, the same degree of hypoxia elicited no changes in LV function. During infusion of V (4 micrograms/min/kg), hypoxia reduced SP10 from 138 to 122 mm Hg (p less than 0.01) and dP/dt10 from 29 to 24 (X 10(2] mm Hg/sec (p less than 0.05). It is concluded that in the absence of adrenergic support, hypoxia significantly depresses both force and velocity parameters of contractility in hearts with calcium channel blockade.

The effect of diltiazem on noradrenaline release

The effects of diltiazem in rat tail arteries and guinea-pig vasa deferentia have been investigated. Superfusion of the rat tail artery with diltiazem (10(-6) - 10(-4) M) resulted in a dose-related increase in 3H-overflow (P less than 0.001) both in Wistar Kyoto (WKY) and in spontaneously hypertensive (SHR) rats. Release of 3H by transmural stimulation (1 Hz, 2 ms, 10 V) was also much greater in vessels perfused with diltiazem; this effect was dose-dependent. Diltiazem did not significantly alter the proportion of noradrenaline and its metabolites in 3H-overflow, as analysed by column chromatography. In the vasa deferentia of guinea-pigs, diltiazem (10(-9) - 10(-5) M) increased spontaneous 3H-release. The results indicate that diltiazem acts on sympathetic nerves and causes the release of noradrenaline.

Propranolol-verapamil versus propranolol-nifedipine in severe angina pectoris of effort: a randomized, double-blind, crossover study

To compare a propranolol-verapamil with a propranolol-nifedipine combination in patients with severe angina of effort, 16 patients (11 men and 5 women, aged 56 +/- 8 years [mean +/- standard deviation]) with more than 5 episodes/week of angina and a positive exercise tolerance test despite propranolol (229 +/- 44 mg/day [range 180 to 360]) were maintained on this dose of propranolol and, in addition, received verapamil (360 mg/day) and nifedipine (60 mg/day) for 3 weeks each in a double-blind, randomized fashion. In comparison with propranolol alone, anginal frequency and nitroglycerin usage were reduced by propranolol-verapamil but not by propranolol-nifedipine. Exercise time (standard Bruce protocol) was similar for the 2 combinations (6.4 +/- 2.0 minutes with propranolol-verapamil, 6.6 +/- 2.1 minutes with propranolol-nifedipine, difference not significant), but the magnitude of ST-segment depression at peak exercise was less (p less than 0.05) during propranolol-verapamil (0.03 +/- 0.06 mV) than during propranolol alone (0.18 +/- 0.07 mV) and propranolol-nifedipine (0.08 +/- 0.07 mV). Left ventricular ejection fraction at rest was higher (p less than 0.05) with propranolol-nifedipine (0.62 +/- 0.10) than with propranolol-verapamil (0.58 +/- 0.10), but neither differed from ejection fraction at rest with propranolol alone (0.59 +/- 0.08). Ejection fraction at peak exercise was similar during all 3 periods. In 2 patients, verapamil caused weakness, lightheadedness, and severe sinus bradycardia (40 to 48 beats/min), and the dosage was reduced (blindly) to 240 mg/day, with the alleviation of bradycardia and associated symptoms.(ABSTRACT TRUNCATED AT 250 WORDS)

Protection of hypoxic myocardium by intracoronary administration of verapamil in open-chest dogs

Hypoxic perfusion of the regional myocardium was performed in 34 open-chest dogs. In eight dogs in which the myocardium was perfused with original hypoxic Krebs-Henseleit (K-H) solution for 5 min (group I) there was a marked decrease in adenosine triphosphate content (2.03 +/- 0.44 mumol/g) and an increase in lactate content (8.65 +/- 2.26 mumol/g). In myocardium of nine dogs (group II) perfused with verapamil-containing (1.3 mg/dl) K-H solution and in that of nine dogs (group III) receiving Ca2+-free solution, the degrees of reduction in adenosine triphosphate (2.99 +/- 0.73 and 3.25 +/- 0.48 mumol/g, respectively) and of lactate accumulation (5.16 +/- 0.59 and 4.79 +/- 1.02 mumol/g, respectively) at 5 min were significantly less than in group I. Absence of statistically significant differences in hemodynamic parameters among these three groups indicates that the metabolic preservation in group II probably resulted from a direct effect of verapamil on the regional myocardium related to Ca2+ metabolism. However, metabolic data in four dogs of group I and four dogs of group III killed at 40 sec of perfusion, in conjunction with results of the analysis of regional contraction, revealed that the time courses of segmental shortening in the three groups did not account for the metabolic differences among them.

The inhibition of Ca uptake in cardiac membrane vesicles by verapamil

Cardiac membrane vesicles take up Ca2+ in response to Na+ gradient (high inside) and negative inside membrane potential. Both components of the Ca2+ uptake, the Na+ gradient dependent uptake and the membrane potential dependent uptake are inhibited by verapamil; the action is dose-dependent and the concentrations of verapamil required to inhibit the Ca2+ uptake to 50% of its maximal value are 50 and 60 microM respectively. In the concentration ranges tested (50-750 microM Ca2+), the inhibitory effect of verapamil could not be antagonized by increasing the Ca2+ concentration of the medium. Introducing verapamil into the vesicles by rapid freezing and slow thawing of the vesicles had the same inhibitory effect as adding the same concentration of verapamil on the outside of the vesicles. Adding verapamil to both sides of the vesicle membrane led to higher inhibition of Ca2+ uptake. It is proposed that addition of verapamil can cause a change in cardiac membranes which is manifested by a decrease in the driving membrane potential and Ca2+ transport.

Randomized, placebo-controlled study of the effect of verapamil on exercise hemodynamics in coronary artery disease

At cardiac catheterization, 16 patients with coronary artery disease (14 men and 2 women) were allocated by a random, double-blind method to intervention with placebo (saline solution) or verapamil (0.2 mg/kg total by bolus and by 10-minute infusion). In all patients, resting and exercise (3 minutes with a bicycle at 150 kg X m/min) hemodynamic values were obtained during a control period and after intervention. Subsequent left ventriculography and coronary arteriography revealed a mean ejection fraction of 52 and 53% and the mean number of diseased vessels (3-vessel scale) of 2.1 and 1.5 in the placebo and verapamil groups, respectively. In both groups of patients, exercise induced significant increased heart rate, mean arterial pressure, left ventricular end-diastolic pressure and cardiac index. Verapamil increased the heart rate and decreased the mean arterial pressure at rest and the arterial pressure during exercise. It did not affect exercise-induced increases in left ventricular end-diastolic pressure or cardiac index. These results support a role for peripheral mechanisms mediating the antianginal effects of verapamil.

The effects of shock energy, propranolol, and verapamil on cardiac damage caused by transthoracic countershock

Myocardial damage by transthoracic countershocks was assessed by observation for electrocardiographic loss of R waves and elevation of ST segments, creatine kinase depletion, and histologic evidence of necrosis in damaged areas, and by excision and examination, 3 days later, of all tissue macroscopically observed to be damaged. When 4000 J of stored energy was passed across the chest of dogs anesthetized with pentobarbital sodium (30 mg/kg), more damage was caused when the energy was divided among 10 shocks than when it was applied in 20 or 40 shocks (at intervals of 0.5 min). The prior intravenous administration of verapamil (1 mg/kg) reduced the weight of damaged shocks. Propranolol (0.4 mg/kg) had no effect. These results give further evidence for the role of calcium accumulation in cardiac necrosis after direct current countershocks. Multiple low-energy shocks cause less cardiac damage than do a few high-energy shocks of similar total energy.

Salutary effects of nitrendipine, a new calcium entry blocker, in hemorrhagic shock

Intracellular accumulation of calcium is thought to play an integral role in the progression of ischemic injury and cell death. We infused the calcium entry blocker, nitrendipine (1.5 micrograms/kg per min), into cats in order to investigate the importance of extracellular Ca2+ influx during hemorrhagic shock. Nitrendipine proved to be a potent hypotensive agent in sham shock cats when infused over a 4 h period (156 +/- 9 to 90 +/- 5 mm Hg) (P less than 0.01). However, in hemorrhaged animals, nitrendipine treatment maintained the post-reinfusion MABP at a significantly higher (P less than 0.01) value than untreated controls (79 +/- 5 vs. 51 +/- 4 mm Hg, respectively). Superior mesenteric artery flow (SMAF) for hemorrhaged animals treated with nitrendipine was significantly higher (9.8 +/- 1.4 ml/min per kg) (P less than 0.01) than that for untreated cats (4.2 +/- 0.4 ml/min per kg), at 2 h post reinfusion. There was no significant increase in SMAF during oligemia in the nitrendipine-treated animals. Nitrendipine was also found to significantly retard the appearance of cathepsin D in the plasma of hemorrhaged cats as well as reduce plasma proteolysis to values not significantly different from sham shock animals. Furthermore, myocardial depressant factor (MDF) activity in the plasma of nitrendipine-treated shock cats was not significantly different from sham shock animals, while the plasma MDF activity for shock cats receiving vehicle increased 3-fold (P less than 0.001). The beneficial effects for nitrendipine in hemorrhagic shock are likely due to both its vasodilator function and its ability to reduce intracellular Ca2+ accumulation during ischemia, thereby reducing disruption of cell membrane systems.

Comparative effects of propranolol and verapamil alone and in combination on left ventricular function and volumes in patients with chronic exertional angina: a double-blind, placebo-controlled, randomized, crossover study with radionuclide ventriculography

With the use of equilibrium radionuclide ventriculography the effects on left ventricular (LV) function of 160 mg oral propranolol daily and 360 mg verapamil daily alone and in combination were compared in 18 patients with chronic exertional angina. A randomized, double-blind, placebo-controlled, crossover protocol was used. The reduction in exercise rate-pressure product induced by the combination (118 +/- 28 mm Hg/min) was significantly greater (p less than .05) than that by propranolol (135 +/- 27 mm Hg/min) or verapamil alone (163 +/- 28 mm Hg/min). In patients at rest, neither single nor combined therapy altered global or regional left ventricular ejection fractions (EFs). Verapamil, but not propranolol, increased (p less than .05) cardiac volumes of resting subjects; used in combination, no further increase in LV volume occurred. With placebo, exercise global EF did not decrease from the level at rest and therefore no drug effect could be demonstrated for this parameter of LV function. By an evaluation of normalized regional EF measurements the combination was shown to reduce exercise-induced hypokinesis (placebo 52 +/- 20%, combination 61 +/- 23%; p less than .01). No significant improvement was noted with propranolol or verapamil alone; only the combination prevented a significant increase in end-systolic and end-diastolic volumes during exercise. Thus, propranolol and verapamil, used alone in moderate doses, exert no beneficial effect on exercise LV function as measured by EF and volume changes, and resting function deteriorates slightly with verapamil.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium-entry blockers and cardiovascular disease

The beneficial effects of calcium-entry blockers in the treatment of ischemia in the heart and in other tissues can be explained by (1) relaxation of venous smooth muscle, in particular that of the splanchnic veins; (2) negative inotropic effect on the myocardial cells; (3) negative chronotropic effects on the heart; (4) inhibition of vasospastic episodes in coronary and other large arteries; (5) depression of myogenic activity and responsiveness to vasconstrictor stimuli in precapillary resistance vessels; (6) inhibition of platelet aggregation; (7) possible increases in the deformability of hypoxic red blood cells; (8) protection of endothelial integrity and function; and (9) protection of the body cells, in particular myocardial cells, from prolonged exposure to anoxia and from massive entry of calcium during reperfusion. In the case of angina pectoris, the effects on the myocardial cells themselves, the decrease in preload and afterload, and the improvement of coronary perfusion combine to allow the heart to perform more work before an imbalance is reached between the metabolic demands of the myocardial cells and their blood supply. The increased myocardial performance may favor collateral circulation and withdrawal of the reflex load upon the heart, originating from the ischemic myocardium. The available calcium-entry blockers vary in their potency to affect the different components of the cardiovascular system.

Role of dimethyl sulfoxide in prostaglandin-thromboxane and platelet systems after cerebral ischemia

Direct and empirical evidence indicates that intravenous administration of DMSO can arrest or reverse cerebral and extracerebral ischemia following experimental or clinical injury. When the delivery of oxygen and nutrients to the tissue is deficient or unavailable (as in ischemia), cell damage or death with all its attending pathological consequences becomes an end-point. In the brain, this equates to build-up of intracranial pressure, impairment of neural transmission to vital centers, and loss of function or death. We have reviewed a number of studies that show the usefulness of DMSO in preventing significant pathology from developing in various experimental injury models and in clinical subjects. We have proposed that the action of DMSO in biochemical, morphological, and functional subsystems is not specific but rather interactive. Figure 5 illustrates this point. Any one effect by DMSO on these subsystems that does not affect the others seems highly unlikely. How DMSO or similar drugs affect these systems, could provide important clues in clarifying the pathogenesis of ischemia and in reducing its severity. We conclude from the available evidence that ischemic injury is a dynamic process constantly promoting biochemical, vascular, and morphological changes and that DMSO is able to intervene at various levels of this pathochemical cascade. DMSO may do this by its ability to normalize tissue perfusion when this is lacking or impaired. We speculate that this effect by DMSO is predominantly on the PG-TX and platelet systems, since these appear to be the most important candidates implicated in vessel occlusion and spasm. It is further concluded from the available and theoretical evidence presented here, that clinical trials using DMSO in cerebral and extracerebral organ ischemia should be designed in order to evaluate the efficacy of this compound to other antithrombogenic therapies. It is reasonable to assume that DMSO may provide a primary approach to the treatment of cerebral, myocardial, renal, and platelet-induced ischemic disorders.

Calcium antagonists and calmodulin: effect of verapamil, nifedipine and diltiazem

The effect of three calcium antagonists (verapamil, nifedipine and diltiazem) on the calcium-induced activation of phosphodiesterase (a calmodulin dependent process) was investigated. Therapeutically relevant concentrations of verapamil, nifedipine and diltiazem were used. In the presence of calmodulin, phosphodiesterase activity was stimulated by calcium in the range 4 X 10(-6)-2.5 X 10(-5) M. Diltiazem (10(-6) M), verapamil (10(-6) M) and nifedipine (10(-7) and 10(-6) M) had no influence on phosphodiesterase activity in the presence or absence of calmodulin at any concentration of calcium employed. By contrast trifluoroperazine abolished the Ca2+ activation of the phosphodiesterase enzyme. From this it is concluded that while the interaction of calcium antagonists with calmodulin may be of interest in the study of the mode of action of calmodulin, it probably does not contribute to their vasodilator activity.

Effect of verapamil on left ventricular function: a randomized, placebo-controlled study

Verapamil has a negative inotropic action in isolated cardiac muscle. Its effects on left ventricular function were tested in 25 patients with suspected coronary artery disease. A double-blind, randomized, placebo-controlled study design was used. Verapamil (0.2 mg/kg over 10 minutes) significantly lowered mean arterial pressure (from 105 to 89 mm Hg) while increasing the cardiac index (from 2.8 to 3.1 liters/min/m2). No statistically significant effect was seen on heart rate, left ventricular end-diastolic pressure or end-systolic volume index, ejection fraction, peak rates of systolic wall thickening or diastolic wall thinning, or percentage of hemiaxial shortening. However, there was a small increase in the left ventricular end-diastolic volume index (from 94 to 102 ml/m2). Important findings were a reduction in systemic vascular resistance (from 39 to 30 U . m2), an increase in left ventricular end-diastolic volume index consistent with a negative inotropic effect, and no evidence of improved regional wall dynamics in portions of the left ventricular wall considered hypokinetic because of myocardial ischemia.